The present invention relates generally to an apparatus for applying a magnetic field to a recording surface of a magneto-optical disk in order to record/erase information thereon/from, and a magneto-optical disk storage having such an apparatus.
In magneto-optical recording, it is necessary to locally heat up a magneto-optical disk by a laser beam to reverse the magnetization while a coercive force Hc is being applied. Hereupon, Japanese Laid-Open Utility Model Application No. 64-42503 has disclosed an apparatus for applying a bias magnetic field, which is the coercive field Hc, to a recording surface of a magneto-optical disk by reversing a permanent magnet in magneto-optical recording/erasing. The apparatus comprises, as shown in FIG.1, a permanent magnet 1, a pair of driving coils 2 and 3, a support plate 5 and a magnetic field detecting means 6. The permanent magnet 1 applies a bias magnetic field, which is the coercive field Hc, to the recording surface 101 of the magneto-optical disk 102. The permanent magnet 1 is flat, located parallel to the recording surface 101, and pivotally supported via an axis 4. The driving coils 2 and 3 are symmetrically located with respect to the axis 4, and are respectively located on the support plate 5 parallel to the recording surface 101. The magnetic field detecting means 6 comprises a hall element. The optical head 103 is located opposite to the apparatus on the other side of the magneto-optical disk 102. When the driving coils 2 and 3 are simultaneously electrified in a direction i.sub.1 or i.sub.2 the apparent magnetic poles, generated on the center lines thereof, pull and repel the magnetic poles of the permanent magnet. Thus, the permanent magnet 1 can be controlled to be rotated by the direction of the current i.sub.1 or i.sub.2. Since the driving coils 2 and 3 are located on the same plane symmetrically with respect to the axis 4, the rotating control of the permanent magnet 1 can be stabilized.
However, the above conventional apparatus has following disadvantages.
1. Since the driving coils 2 and 3 are located in parallel, the apparatus cannot be miniaturized, and thus the apparatus cannot be used for an magneto-optical disk smaller than 3.5 in.
2. Since the magnetic poles of the permanent magnet 1 are too far from the apparent magnetic poles, the rotating of the permanent magnet 1 cannot be controlled with a response time of less than 10 ms. That is, as shown in FIG.2B, if the current is turned off after the driving coils 2 and 3 are electrified and thus the permanent magnet 1 is reversed, the permanent magnet 1 traces a damped oscillation curve shown in FIG.2A so that a settling time takes more than 15 Ms. Hereupon, the term "a settling time", as used herein, means the time for the permanent magnet 1 to reverse and halt.